1. Field of the Invention
The invention is concerned with the testing of electrical conductor elements in the manufacture of integrated circuit devices.
2. Description of the Prior Art
Electrical conductor elements such as gold, aluminum, or suitably doped silicon stripes deposited on a substrate are commonly used in integrated circuit devices to electrically connect active and passive circuit components. Such elements typically have a thickness on the order of a fraction of a micrometer and a width on the order of a few micrometers and, consequently, can be inspected visually only by means of magnifying equipment such as a microscope. Moreover, visual inspection is too time-consuming to be practical in the context of large scale industrial production of integrated circuitry.
While gross defects such as discontinuities in conductor stripes become manifest immediately upon functional testing of a circuit, other defects may go undetected initially but may yet result in premature failure of a device in use. To identify such potentially short lived conductor elements, a so-called third harmonic method has been proposed for testing conductor stripes. This method is based on the observation that conductor stripes which are prone to fail, e.g., due to nonuniformity of width, thickness, composition, or adhesion to the substrate, typically exhibit nonlinearity of resistance as a function of current. According to the third harmonic method a fundamental sinusoidal signal is applied to a linear AC-coupled network across whose output terminals the conductor element to be tested is placed. By measuring the amplitude of the third harmonic component of the output signal a measure for the nonlinearity of resistance of the circuit element is obtained. Successful application of this method is described in "The Non-linearity of Fixed Resistors" by P. L. Kirby, Electronic Engineering, November, 1965, pages 722-726, and in "Harmonic Testing Pinpoints Passive Components Flaws" by Vilhelm Peterson and Per-Olof Harris, Electronics, July 11, 1966, pages 93-100. However, due to the need for a signal generator which produces a signal of extremely low harmonic contents, test equipment implementing the third harmonic method tends to be complicated and poorly suited for use in the large scale testing of integrated circuitry.